1. Field of the Invention
The present invention relates generally to disc cartridges and, more particularly, is directed to a disc cartridge in which a disc-shaped record medium such as a magneto-optical disc or the like is accommodated in the state that the record medium can be recorded and/or reproduced.
2. Description of the Prior Art
Recently, a magneto-optical disc (hereinafter referred to as an MO disc) and an optical read-only memory (hereinafter referred to as an O-ROM disc) are available as an optical disc of 90 mm-type. These optical discs are accommodated in a disc cartridge and can be recorded and/or reproduced by a head apparatus through an openable and closable opening portion by a shutter which is formed on the disc cartridge.
Let us explain a prior-art disc cartridge which incorporates therein a 90 mm optical disc according to the ISO standard. FIGS. 1 to 3 show an example of such a disc cartridge.
As shown in FIGS. 1 to 3, there is shown a cartridge body 1 which is formed of an upper cartridge half 1a and a lower cartridge half 1b. A window aperture 2 is formed through the upper half 1a at its lower corner, whereas a rectangular window aperture 3 is formed through the lower cartridge half 1b. This rectangular window aperture 3 is formed of a window aperture portion 3a corresponding to the window aperture 2 and a window aperture portion 3b which is not corresponding to the window aperture 2. This rectangular aperture 3 is twice as long as the window aperture 2 in the length direction. A closing member 4 the size of which is 1/2 of that of the rectangular aperture 3 is movably engaged with this rectangular aperture 3 between the one half portion 3a provided as the corresponding portion and the other half portion 3b provided as the non-corresponding portion, thereby the closing member 4 being changed-over from the outside into the window aperture portion 3a or 3b serving as identification means.
The identification of the optical disc incorporated in this disc cartridge is performed by detecting the switching position of the closing member 4 engaged with the rectangular opening portion 3. The position of the closing member 4 is mechanically and optically detected.
From a mechanical standpoint, as shown in FIG. 2A, a recording and/or reproducing apparatus (not shown) is provided with a push-type switch 5 having a pair of operation members 5a and 5b which are corresponding to the one half portion 3a and the other half portion 3b of the rectangular opening portion 3 of the cartridge body 1. Accordingly, under the condition that the disc cartridge is incorporated into the recording and/or reproducing apparatus, the closing member 4 pushes the operation member 5a or 5b (in FIG. 2A, the operation member 5b being pushed) thereby the position of the closing member 4 being detected mechanically.
From an optical standpoint, as shown in FIG. 2B, the recording and/or reproducing apparatus is provided with a light source 6 such as a light emitting diode (LED), lamp or the like corresponding to the window aperture 2 of upper half 1a of the disc cartridge body 1, whereas in the recording and/or reproducing apparatus photo detectors 7a and 7b are respectively provided in facing relation to the one half portion 3a and the other half portion 3b of the rectangular window aperture 3 formed at the rear surface side or the lower cartridge half 1b. Under the condition that the disc cartridge is loaded onto the recording and/or reproducing apparatus, the closing member 4 is opposed to the photo detector 7a or 7b (photo detector 7b in FIG. 2B) so that the light emitted from the light source 6 can not be received by the photo detector 7b, thereby the position of the closing member 4 is detected.
When the closing member 4 is removed from the rectangular window aperture 3 of the cartridge body 1, the rectangular window aperture 3 is opened so that the position of the closing member 4 can neither be detected mechanically nor optically.
As described above, in this disc cartridge, different pre-determined information can be obtained on the basis of the positions of the closing member 4, i.e., as shown in FIGS. 6A and 6B. Three modes of the closing member 4 relative to the rectangular opening 3 of the cartridge body 1 are used to identify the kinds of discs incorporated in the disc cartridge. The identification is performed with respect to the existence or absence of the write-protect of the MO disc and the kind of the MO disc.
As described above, in the prior-art disc cartridge, the three kinds of identification such as the existence or absence of the write protect mechanism and the kinds of discs such as the O-ROM disc or MO-disc can be performed by the appearance of the disc cartridge. However, the prior-art disc cartridge cannot perform other necessary identification such as whether a reflecting layer is a layer having high reflectivity formed of an aluminum film or the like in the case of the O-ROM disc, whether the reflecting layer is a layer having low reflectivity corresponding to the MO-disc and whether the byte number per sector is 512 .sup.BYTE /Sector or 1024 .sup.BYTE /Sector or the like.
Accordingly, in order to determine whether the reflectivity of the O-ROM disc is high or low, a sample laser light must be irradiated on a particular portion of the disc and the magnitude of amount of the reflected-back light must be detected. In the above-mentioned operation, when the MO disc is accommodated into the disc cartridge, there is then the risk that the data is destroyed. Further, if the identification is performed at the unit of byte number per sector, data of particular zone of the disc is read-out.
As described above, data, which can not be read out from the external appearance of the disc cartridge, is determined by an electrical circuit and hardware in the recording and/or reproducing apparatus so that the burden on the electrical circuit and the hardware becomes considerably larger.